1. Field of the Invention
The present invention relates to a position detection method and, more particularly, to a method which is suitably used for an exposure apparatus for protecting and transferring a pattern on a reticle onto a photosensitive substrate in the manufacture of semiconductor integrated circuits, liquid crystal display elements, and the like.
2. Related Background Art
In an exposure apparatus of this type, a so-called baseline measurement for measuring the relative positional relationship between a reticle alignment device for aligning, e.g., a reticle, and a substrate alignment device for aligning a photosensitive substrate using an absolute coordinate system in the exposure apparatus, is performed prior to exposure. In general, the baseline measurement is achieved in such a manner that a reference mark formed on a stage is detected by a reticle alignment microscope of the reticle alignment device to measure the detection center position of the reticle alignment device on a stage coordinate system, and the reference mark on the stage is detected by a substrate alignment microscope of the substrate alignment device to measure the detection center position of the substrate alignment device on the stage coordinate system. In this case, the moving coordinate system of the stage on which the reference mark is formed serves as an absolute coordinate system in the exposure apparatus.
As the reticle alignment device and the substrate alignment device, devices which use pattern matching image processing are known. In order to use a new alignment device adopting the pattern matching processing in the exposure apparatus, baseline measurement must be performed to obtain the relationship between the detection center position of the alignment device and the absolute coordinate system (stage coordinate system) in the exposure apparatus.
In a position detection method based on pattern matching, an image S to be processed including a mark M, as shown in FIG. 4, is searched to find a position matching a template image T formed with the same mark TM as the mark M, as shown in FIG. 5. In this example, as a pattern matching processing result, a position R1 in the image to be processed, which corresponds to an origin O1 of the template image T, is obtained.
Note that a measurement result required upon execution of the baseline measurement is the value of a center iR of the mark M shown in FIG. 4, which corresponds to a center TS1 of the mark M1 in FIG. 5. In other words, the measurement result required upon execution of the baseline measurement is the position, in the image S to be processed, of the center iR of the mark M. However, since the template image T is an image fetched from an actual image into a pattern matching device by appropriately changing its size so as to include the mark TM, there is no method of detecting the position of the mark TM in the frame of the template image T. Therefore, the position of a point R1 in the image S to be processed can be detected, but the position, in the image S to be processed, of the center iR of the mark M cannot be detected.
Therefore, the relative positional relationship between the reticle alignment device and the substrate alignment device, i.e., the so-called baseline, cannot be accurately measured.